Signal generator



J. L. FINCH SIGNAL GENERATOR Fne'dF'eb. 24, 1940 March 2, 1943.

5 Sheets-Sheet 1 INVENTOR. A JAMES L. FINCH ATTORNEY.

M'mh 2, 19.43. J. L FINCH 2,312,810.

SIGNAL GENERATOR Filed Feb. 24, 1940 ls sneets-shet-z till t Il" INVENTOR. JAMES L. FINCH W Wm.

Mmh z, 1943'.

J. L. FINCH SIGNAL GENERATOR Filed Feb. 24. 1940 3 Sheets-Sheet 3 v mm n mm m ,w/ffn Is .A H i/ v. B 2 mib".

Patented Mar. 2, 1943 2,312,810 SIGNAL GENERATOR James L. Finch, Patchogue, N. Y., assigner to Radio Corporation of America, a corporation of Delaware Application February 24, 1940, Serial No. 320,523

(Cl. Z50-36) v V19 Claims.

This invention relates generally'to a keying system, and more particularly to a signal generator for producing an audio frequency wave which is interrupted or ychopped up into characters. The signal generator with which this invention is particularly concerned will hereinafter be referred to as a tone signal generator.`

Heretofore, in checking or testing the performance of a locally situated transmission system it has been customary to transmit from a remote central oce over a land line energy in the form of a tone or alternating current corresponding to certain signal characters. Such a system requires the use of terminal apparatus at the remote central ofce as well as a control channel extending from thecentral oilice to the local radio transmitting system. The terminal apparatus at the remote central oii'ce may consist of a facsimile machine or a high speed automatic transmitter, or other suitable apparatus. The procedure which has been followed in such known systems has required that information be relayed from the attendant or operator at the local transmitting system to the remotely situated central oflice to the effect that checking or testing of the transmitting system is necessary. Upon receipt of this information at the remotely located central cnice, the checking or testing equipment at this central office would be placed into operation. j

VThe present invention eliminates the need for remotely situated character transmitting or checking apparatus for testing purposes and also eliminates the need for a control channel, by providing suitable means which can be used at the local transmission system for generating the desired signal characters.

One of the objects of the present invention is to provide a tone signal generator for producing an audio frequency wave interrupted or chopped up into characters, wherein the characters may have any desired weight and may employ any desired wave frequency within a wide range.

Another object of the present invention is to provide a source of continuously repeated signal characters consisting of mar g characters and spacing characters, the marking characters being composed of any one of a group of selectable audio frequency Waves.

A further object of the present invention is to provide a source of continuously repeated signal characters consisting of marking characters and spacing characters, the marking characters being adjustable in length or weight with respect lestablishing the frequency to a complete cycle of operation composed of both a marking and a spacing character.

Other objects and their advantages will appear from a reading of the following description which is accompanied by drawings, wherein:

Fig. 1 villustrates a complete tone signal generator in accordance withfoneembodiment of the present invention; Y

Fig. 2 is a graphical representation given to aid in understanding the operation of the system of Fig. 1;

Fig. 3 showsa dial employed in connection with the relaxation oscillator of the tone signal generator of the invention; and

Fig. 4 is a preferred form of tone signal generator embodying the principles of the invention.

The tone sign-al generator of the invention shown in Fig.` 1 includes a relaxation oscillator I, a character chopper 2, an audio frequency oscillator 3, and a keyed amplifier 4, all coupled together in a manner more fully'described here-- inafter. Y y

A suitable power unit 5 comprising a pair of transformers T1 andTz whose primary windings are coupled'to a source of 110 volt-60 cycle Vsupply,l a full -v'vavefrectilier R,'and a low pass lter F for smoothing out the ripplesfrom therectier, servesto supply suitable polarizing potentials and heating currents for the electrodes of 'the vacuum tube elements' of the tone signal generator.A Y f L The relaxation oscillator I comprises a gridcontrolled glow discharge tube I2, sometimes known as a thyratron, having -anindirectly heated cathode K. aV grid G and an anode A. The grid, anodeand cathode velectrodes of the glow'tube I2 are connected to suitable points on a voltage divider comprising' resistors 8, 9 and I0 connected across the positive and negative terminals of the power uniti, as shown. An adjustable condenser I4 composedof a plurality of selectablercondenserA units is connected across the cathodeK and anode Aof thel glow tube'for of oscillation of the relaxation oscillator. Other elements for the establishment of the frequency of 'this relaxation oscillator-are the serially connected resistors I5 and I6 which are connected between the cathode K and the grounded or unit. It willbe appreciated that th'e relaxation oscillator operates yat audio frequencies, and more specifically at character frequencies, i. e., keying frequencies, and produces saw-tooth waves. The adjustable condenser unit I4 is driven by al shaft to which is connected a dial 6 for indicating negative side of thepower provided in the which one of the several capacitors of the condenser I4 is connected in the circuit, thus indicating the range of audio frequencies within which the oscillator is operating. The resistor I' is adjustable and is provided with a dial l, shown in more detail in Fig. 3, for indicating the exact frequency of oscillation in the range selected by dial I5; An inductive reactor I3 is provided in series with the anode lead for limiting the instantaneous current through the tube I2 to a suitable value. Similarly, the resistor II is grid circuit to limit the grid current of the tube In parallel relation frequency of the relaxation frequency oscillator due to effects in the output of manner to be described later. The output of the relaxation oscillator I, which in eect isthe voltage across condenser I4, is impressed upon character chopperunit 2.of the tone signal generator.

The character' chopper unit 2*.includes agridcontrolled glow discharge device I-I having an indirectly heated cathode vK,a grid G' and an anode A'. The cathode K of this tube is directly connected to thecathodeKof the relaxation oscillator, both cathodes being connected 'in parallel to the samepoint' onY resistor I5. The grid G of character chopperII is connected through a resistor 22 to a slider on a potentiornf eter I9. Potentiometer I9 together with serially connected resistors 2! and 2 Iform a voltage divided which is connected across two sides of the power unit in a mannerv similar to voltage divider 8, 9 and ID. Y I2and so arranged that the output of the relaxation oscillator is impressed during a portion of each cycle across resistor IB-in the anode circuit of the character chopper. lhecharacter chopper .functions to key or control the keyed amplifier 4, from the latter of which characters of Square formation are obtained in the output. l

Keyed amplifier 4 is arpush-pull amplifying system comprising a pair of indirectly-heated cathode Vacuum tubes 33A andbwhosecathodes are connected in parallel to a slider 5I! onM resistor infthevoltagedividersystem- I9, `20 and ,2I.` 'Thel grids of the amuplier tubes are `connected together through-.resistors 35V and 36 from whicha connection is made to the, anode A. of the character chopper tube lI 1 `These same grids of the amplifier .arealso connected to one winding of an audio transformer 32 to f whose other winding vis suppliedan audio frequency wave from the audiooscillator 3. In the output of the keyed amplifier `there is provided a rethe chopper in the to a Value which is not excessive., Y to resistors I5 and It there are provided a pair of serially connected resistors l5 and 4B for compensating for variations inthe 'Y the audio Voscillator Tube I'Il is similar to tube sistor or potentiometer 3I to which is connected a slider 43 whichvis adjustable over 31 to reduce to ,a minimum the transients ,inthe output terminals due to the anode current of tubes 133 and 34. An instrument 41 is serially connectedy in the circuit from slider43 to thel positive side of the powerl unit to indicate the percentage of marking time to the total time. The output from the keyed amplifier isfpassed through an audio frequency transformer 38 to suitable jacks 40 and 4I from which connections extend through suitable apparatus to any desired type of utiliza'- tion circuit; for example, atonesignal converter which, in turn, is used'forkeying a radio Ytransmitter. PotentiometerY 3S is employed for controlling the volume of the ,output of the keyed amplifier. `1 l 4Audio :oscillator-..3 comprises 4an .indirectlyof scales `passes through audio and through the normally made contacts of jack having an auxiliary heated cathode vacuum tube 23 having a tuned circuit comprising an adjustable condenser 28, adjustable by selecting any one of a plurality of individual condensers or groups of ccndensers in parallel relation to one winding of the audio frequency transformer 24. The other winding of transformer 24 is connected to the grid of the tube 23 through a grid leak condenser combination 25. Transformer 24 is preferably a specially designed transformer having large leakage re actance. The output of the audio oscillator 3 frequency transformer 29 3Q before being impressed upon audio transformver 32. It will be evident that if desired a plug audio tone may be inserted into jack 30, thus breaking the connection from y 3 to the keyed amplifier 4 and connecting thekeyed amplifier 4 to the auxiliary tone input.

The operation of the systemwill now bedescribed. Considering the relaxation oscillator, .the voltage across resistors 9 and I0 is impressed ,across the circuit comprising condenser I4 and serially arranged resistors I5 and IG. Let us consider the start of the cycle to be the 4time when thereis no charge on condenser I4. Charging current for condenserV vIll will vthen flow through resistors I5 and I6 tending to charge the condenser I4 to the full voltage of the source. The gaseous grid-controlled glow tube or Vthyratron I2 hasitsanode A and cathode K connected across condenser I4 while itsgrid G is connected through resistor II to the junction point 61 between resistors 9 and I0. At the start of `the cycle, the cathode K of tube I2 will be more positive than the grid G of this same tube. Consequently no Current will flow through the glow ltube. Asv the condenser .I4 charges up,rhowever, the voltage on the cathode Kbecomes more nega'.- tive-relative to the anode and the grid and even- ,tually becomes G. When a particular Voltagerelation between ,the'cathode K `and the grid G of the glow tube I2 is reached, the glow in the tube will strike and .the cathode-anode circuit of tube I2 becomes highly conductive. This condition of the glow tube permits Athe condenserA Y I4 to discharge through the tube I2 veryAquickly, after which the cycle of operations describedabovewill re'- peat it-self. V

The ,frequency of oscillation of the relaxation ,oscillator I may vIce increased .by decreasing the capacity'of condenser I4 or by decreasing the resistance of resistor IS, while rthe frequency of oscillation can be reduced byincreasing the oapacity of condenser` I4 or by increasing the resistance of resistorY I6. The switch of condenser I4 is connected tothe dial 6 which, as mentioned before, has an indicator which indicates the range of frequencies in which the relaxation oscillator is to operate. Resistor I6, on the other hand, is linked to dial I which isprovided with a plurality each scale .indicating the exact frequency withintlie selected range of dial 6. Both dials 6 and 1 must be read `together to obtain a correct indication of the frequency of the oscillator (note'Fig. 3).

At the beginning of the cycle assumed above, the voltage relation between the vcathode K of the-character chopper tube-I'I'and the point 2l .between potentiometers AI9 and 20 is such that .the glow tubeV I1 is non-conducting. In this connegativeV with --respect to the grid comes more negative relative to the anode A of tube I1, it will be obvious that in eiect the voltage on the anode A' becomes more positive relative to the cathode K.- Potentiometer I9, to which the grid G of glow tube I1 is connected, is so set lby means of the slider that at the start of the .cycle the grid G' is more negative than the cathode K. At some point in the cycle of operation the cathode K will attain a Voltage with respect to the grid G such that the glow in the tube I'I will strike Iand the anode-cathode circuit will become conductive. This `point in the cycle is variable and is determined by the position of the slider on the potentiometer I9. When the glow tube I1 -becomes conductive, the output voltage of the relaxation. oscillator, which is across condenser I4, is impressed upon resistor I8, except for the constant voltage drop of the glow tube I1 and except for the voltage diierence across resistor 8 and resistors 20 and 2I- This condition continues until condenser I4 discharges at the end of the cycle.

At this time it should be noted that in these circuits the glow tubes I2 and I1 of Fig. 1 diier in operation from grid-controlled glow discharge tubes in conventional circuits, in rthat in the present invention the circuits cause :both -the bias grid-cathode voltage and the anode-cathode voltage to change, while in the conventional circuit only the anode-cathode vol-tage changes while the bias grid-cathode voltage is constant.

The operation of the system, as so far described, will ybe more clearly understood by reference to Fig. 2 which graphically represents the wave form of the potential generated in the glow tubes I2 and Il. 'Ihe ordinate represents the voltage E while the abscissa represents the time relation t. The start of the cycle when glow tube I2 is non-conducting is represented by point P at time t'. As the condenser I4 charges up, the cathode voltage becomes more negative relative to the anode vand will tend to follow the logarithmic curve X, .partly shown by the dot and dash line, which slopes gradually down to meet the abscissa axis t at some remote point. However, when the voltage on the cathode bears a predetermined relation with respect to the grid which will occur when the cathode is negative with respect to the grid or nearly zerowvith respect to the grid depending upon the characteristics of the tube employed, the glow in the tube I2 will strike at a point represented by P on the curve X at time interval t". At this point the vol-tage'Em .frompoint P' to point P along the vertical axis represents the voltage on the condenser I4 while the voltage E15, 1c from point P on the vertical axis to the abscissa represents Voltage across the resistors I5 and I6. In referring to this point P at this time it is assumed, of course, that point 'P now represents a horizontal voltage line atthe distance P above the time axis. The discharge of the condenserl I4 through the glow tube which occurs at point P will cause the wave form to rise up again to a point on the P line, and the same cycle of operation will repeat itself. `Considering the operation of character chopper 2, when the wave form of the glow tube I2 has reached point P, representing the start of the cycle, the voltage across the anode A" and cathode K of tube I'I will be substantially the same as the voltage across the anodey A and cathode K of tube I 2. This voltage on the. anode and cathode of tube I'I is represented by the line E27, x' and is shown to be slightly higher than the voltage on the same electube. This voltage is represented trodes ofV tube I2 because of certain constants chosen in one particular embodiment ofithe invention, although it should be understood that the voltage on the anode-cathode electrodes of tube I'I may be the same or even less than the corresponding voltage .on the glow tube I2. As the cathode voltage of the tube I2 becomes more negative with respect to the anode, the tube Il' willv be non-conducting until time t" is reached, at which time the relative voltage between cathode and grid of tube I'Iis such that the -glow in tube I'I strikes, after which the glow tube I1 will be .conductive luntil time t is reached. It should be notedthat during the interval between t" and 15 the voltage across the anode and cathode of tube I'I is substantially constant and equal to the glow sustaining voltage in this same by EA'K'.; The voltage across resistor I8 resulting from the ow of current through resistor I8 and the anode` cathode circuit A', K of tube I'I at any time is indicated by the vertical line E1s. The conductivity of glow tube Il will cease immediately upon the complete discharge of condenser I4 through tube I2, a feature which the cycle of operations in both tubes I2 and I7 will repeat in the manner described above.

Currents flowing through the anode-cathode circuit of tube I'I will tend to influence the frequency of the relaxation oscillator. When these currents are varied with respect'to their duration by varying the weight of the characters by means of potentiometer I9, this tends to change the frequency of the relaxation oscillator. To compensate for this change, resistor 46 is caused to vary by the same control means as that used to set the slider on potentiometer I9. multaneous variation is Veitected by unicontrol shaft 42, represented by dotted lines. Thus', when the frequency Aof the relaxation oscillator I tends to increase due to this cause, resistor 46 is increased and produces a counter tendency to decrease the frequency of the relaxation oscillator.

When the glow tube I'I is in a non-conducting condition during the time interval between t" and t" of Fig. 2, the bias on the grids of the keyed amplifier tubes 33 and 34 is determined by the position of the slider 5I! on the potentiometer 20, at which time tubes 33 and 34 are conducting and passing audio frequency tone out to a suitable utilization circuit. However, when glow tube I'I becomes conducting during the time interval between t" and t"", this bias on vace uum tubes 33 and 34 of the keyed amplifier 4 is increased by the voltage which is impressed upon resistor I 8 represented by E18 in Fig. 2. For all operating adjustments, this voltage impressed upon resistor I8 is suicient to block vacuum tubes 33 and 34 as soon as tube I 1 bef comes conducting, thus preventing tone from going out over jacks 40 and 4I. In this manner output current flows from the keyed amplifier 4 or, putting it another way, a marking character is formed during the interval between time t and t", while a spacing character is formed during the time interval between t'" and tf-TL These marking and spacing characters can .be varied to take any desired interval between t and tentiometer I9.

In the operation of the tone signal generator as a whole, the adjustable condenser 28 of the audio oscillator 3 is set for thedesired 'audio fre;- quencyand dial 6 and dial 'I-are'set to VYgive the t"" by adjusting popercentage of vtime relaxation frequency or frequency of repetition of the marking and space, while potentiometer I9 is set to give the desired weight or mark. By means of this adjustment kof potentiometer I9, efected by movement of the slider due to movement of the unicontrol means 42, the weight (i. e., the length) of mark can be adjusted to be anywhere from say 5% to 95% of the character cycle, taking place during the time interval between t" and t". For the purpose of calibration of the percentage marking instrument 41, the potentiometer I9 is first set at its lowest position so as to give an uninterrupted tone output from the signal generator, i. e., con'- tinuous mark. (This occurs when tube I1 will be continuously non-conducting.) Potentiometer 20 will now be adjusted until instrument 41, which is in the anode supply lead to the keyed amplifier 4, has a defiection mark of 100%, after which the unicontrol means 42 will be adjusted to vary the potentiometer I9 until the instrument 41 indicates the percentage which it is desired the marking time should bear to the total time of the character. After all this has -been done, potentiometer 39 is adjusted to the desired output level.

Fig. 3 shows in detail one form of dial 1 which may be used in the relaxation oscillator circuit for resistor I6. There may be one such dial, as shown in this figure, for each setting of dial 8. This dial comprises a pointer 2S secured to a knob 48 which is movable over several stationary scales 49, 5l and 52, each of the latter having engraved thereon around the periphery different frequency markings. Where the switch on condenser I4 produces by movement thereof frequencies which are dissimilarly related to each other, then a single dial 1 (such as shown in Fig. V3) `may be used for two or more settings of the dial 6, in Ywhich case it will only be necessary to multiply cach of the markings on the stationary scale by ten or one hundred.

Fig. 4 shows a preferred form of the invention which is almost identical with the system of Fig. 1, except for a few minor changes which will appear hereinafter. The operation of this system of Fig. 4 is substantially the saine as the operation of the system of Fig. 1, and the same reference numerals (some with prime designations) are employed in both of these figures to indicate equivalent parts. The main differences between the system of Fig. 4 and the system of Fig. 1 lies in the use of a buffer vacuum tube amplifierl stage 53 placed between the output of the relaxation oscillator l and the character chopper 2. This buffer amplifier has its anode connected on the one hand through a resistor 54 to a voltage divider 55 and the same anode is connected on the other hand through a connection 56 to the cathode of the glow tube l1 of the character chopper 2. The relaxation oscillator shown in Fig. 4 is of the conventional type wherein the bias grid-cathode voltage is constant, the only voltage which changes being the anode-cathode voltage. A voltage regulator tube 51 ensures substantially constant supply voltage to the relaxation oscillator. The lkeyed amplifier V4 is here shown as a single evacuated vessel Acontaining therein a pair of push-pull operated electrode structures, the cathodes being connected to the voltage divider by means of slider 50. In this case, however, the nal bias adjustment for the keyed amplifier` is obtained by means of slider 58. There is some -further ydifference in the manner in which the audio oscillator 3 .supplies audio frequency waves to the keyed amplifier, butinasmuch .as this difference is @somewhat conventional and apparent to anyone skilled in the .a-rt, it is not believed necessary to describe the same inv any detail. The audio frequency oscillator 3 of Fig. 4 differs somewhat from Vthe audio oscillator 3 of Fig. 1. In Fig. 4 this audio `oscillator comprises a vacuum tube 23 having a pair of anodes, apair of grids, and a pair of cathodes,.and a tuned circuit consisting of reactor 24 in parallelrelation to any one of the group of selectable eondensers forming a condenser 28. VThe tuned circuit 24', 28 is connected across both anodes of the vacuum tube 23. One grid of this tube is directly connected to ground while the other tube is connected to ground through a pair of resistors 59 and 6D. Both cathodes are directly connected together and to ground through a resistor BI'. The output voltage from the audio frequency oscillator 3 appears across resistor 60 and is taken off by means of connection 6I to be applied to one winding of transformer 32'. A-condenser 62 connects the ungrounded grid to the anode directly associated with the other grid. Condenser 63 is a by-pass condenser for audio frequency energy connecting one of the anodes as well as one side of the tuned circuit to ground. A positive polarizing potential for the anodes is supplied by connection 64 which extends from the oscillator 3 to the power unit. A plurality of resistors are shown individually associated with different condenser units of the condenser 28 and serve for the purpose of reducing the power output level at different frequenciesv to substantially the same value. A jack 65 is -provided in the output of the keyed `amplifier and vhas short circuited contacts in series with the output of the keyed amplifier 4' for the purpose of enabling the attendant to key the system by hand in the event it is desired to communicate over the controlled transmission system with a remote receiving point. In such a case the tone signal generator will be adjusted for mark, that is a continuous transmission of tone signal characters without any interruption, land the attendant, by

means of a plug to be inserted in jack 65, can key the outgoing circuit, thus usingthis tone signal generator merelyl as a source of carrier tone.

What is claimed is:v

1. In combination, a relaxation oscillator, an amplifier, an audio frequency oscillator whose output is coupled to the-input of said amplifier, an electric tube coupling said relaxation oscillator and said amplifier and A*responsive Vto lthe operation of said lrelaxation oscillator for periodically interrupting the output from said amplifier, whereby there are produced signal characters 'in accordance with said interruptions, and means for controlling the weight of said signal characters.

2. In combination, a relaxation oscillator, an amplifier, an audio frequency oscillator whose output is coupled to 4the input of said amplifier, an electric tube coupling said relaxation oscillator and said `amplifierand responsive to the operation of said relaxation oscillatorv for periodically biasing said amplifier to cut-off, whereby there vare produced tone signal characters in the output of said amplifier, and means in circuit with said electric tube lforadjusting the'weight of said tone signal characters.

3. In combination, a gaseous discharge tube relaxation oscillator having means for controlling the frequency of the'j l'produced oscillations, 'an amplifier, an audio Yfrequency oscillator having means for varyingthe frequency thereof, a connection from said audio oscillator to the input of said amplifier, and a non-oscillatory gaseous d ischarge tube circuit coupling said relaxation oscillator and said amplifier for periodically interrupting the conductivity of said amplifier during a predetermined portion of the cycle of operation of said relaxation oscillator.

4. In combination, a gaseous dischargetube relaxation oscillator having means for .controlling the frequency of the produced oscillations, an amplifier, an audio frequency oscillator having means for varying the frequency thereof, a connection from said audio oscillator tothe input of said amplifier, a non-oscillatory gaseous discharge tube circuit coupling said relaxation oscillator and said amplifier for periodically interrupting the conductivity of said amplifier during a predetermined portion of the ycycle of operation of said relaxation oscillator, and a buffer amplifier between said relaxation oscillator and said non-oscillatory gaseous discharge tube. Y if 5. In combination, a gaseous discharge tube relaxation oscillator having means for controlling the frequency of the produced oscillations, an amplifier, an audio frequency oscillator having means for varying the frequency thereof, a connection from `said audio oscillator to the input of said amplifier, a non-oscillatory gaseous discharge tube circuit coupling said relaxation oscillator and said amplifier for periodically interrupting the conductivity of said amplifier during a predetermined portion of the cycle of operation of said relaxation oscillator, and a resistor coupled to the electrodes of both said' gaseous discharge tubes for compensating for any tendency on the part of the relaxation oscillator to change its frequency due to reaction caused by said non-oscillatory discharge tube 6. In combination, a gaseous 4discharge tube relaxation oscillator having means for controlling the frequency of the produced .oscillations, a push-pull audio frequency amplifier, an audio frequency oscillator having means for varying the frequency thereof, connections .loetween said audio oscillator and the input of said push-pull amplifier, and a non-oscillatory gaseous discharge tube circuit coupling said relaxation oscillator and said amplifier for periodically biasing said amplifier to cut-ofi' in dependence upon the cycle of operations of said relaxation oscillator, said amplifier being biased to cut-off during the time said non-oscillatory gaseous tube is conductive and vice versa.

7. In combination, a gaseous discharge tube relaxation oscillator having means for controlling the frequency of the produced oscillations, an amplifier, an audio frequency oscillator having means for varying the frequency thereof, a connection from said audio oscillator to the input of said amplifier, a non-oscillatory gaseous discharge tube circuit coupling said relaxation oscilaltor and said amplifier for periodically interrupting the conductivity of said amplifier during a predetermined portion of the cycle of operation of said relaxation oscillator, and a potentiometer in the output of said amplifier for controlling the volume of the energy in said output.

6. In combination, a gaseous discharge tube relaxation oscillator having means for controlling t-he frequency of the produced oscillations, a push-pull audio frequency amplifier, an audio frequency oscillator having means for varying the frequencythereof, connections, between said audio oscillatorand the input of -said push-pull amplifier, a non-oscillatory gaseous discharge tube circuit coupling said relaxation oscillator and said amplifier for periodically biasing said amplifier to cut-off in dependence upon the cycle of operations of said relaxation oscillator, said amplifier being biased to cut-off during the time said non-oscillatory gaseous .tube is conductive and vice versa, means in the output of said push-pull amplifier for reducing to a minimum the transients due tocurrents in said amplifienand means ,for controllinggthe volume of the output of said amplifier.'

9. In combinatiom-a relaxation oscillator comprising a gaseous discharge tube having across its anode and cathode anadjustablecondenser composed of a plurality of selectable-condenser units, anamplifier, an audio frequency oscillator having a tuned circuit composedof an inductive reactor and in shuntthereto an adjustable vcondenser vcomprisedl of a plurality of selectable condenser units, a connection from the output of said audio oscillatorto the input of said amplifier, an electric tube coupling said relaxation oscillator vand Asaid amplifier andresponsive to the operation of said relaxation oscillator for periodicallyinterruptingthe output from said amplifier, whereby there are produced signal characters in accordance with said interruptions, and means for controlling the weight of said signalcharacters. l y

10. In combination, a 1 relaxation oscillator comprising a gaseous discharge tube having across its anode and cathode an adjustable condenser composed of a plurality of selectable vcondenser units, an amplifier, an audio frequency oscillator havinga tuned circuit composed of ,an

inductive reactor and in shuntthereto an adl Weight of said signal characters.`v` A 11. In combination, a relaxation oscillator comprising a gaseous discharge tube having across its anode and cathode an adjustable condenser composed of a plurality of selectable condenser units, a source of direct current voltage having one side connected to one terminal of said adjustable condenser and the other side connected through an adjustable resistor to the other terminal of said adjustable condenser, whereby both said adjustable resistor and said adjustable condenser establish the frequency of oscillation of said relaxation oscillator, a dial linked to said adjustable condenser for indicating the range of frequencies within which said relaxation oscillator is operating, and a dial linked to said adjustable resistor for indicating the exact frequency of oscillation in the range y selected by said first dial, an amplifier, an audio frequency oscillator Whose output is coupled to the input of said amplifier, an electric tube coupling said relaxation oscillator and said amplifier and responsive to the operation of said relaxation o'scillato'rf for "periodically interrupting. the"u out# put? from said amplifier; whereliyithere are pro; duced'fsignal characters' in accordance withsaid interruptions; and? meanslforcontrolling' the Weight'of-said signalcharacters.A v

l2; Incombination? a-sawtooth wave generator, ani amplifier, mean'sf'couplingi said generator andthe-input of'said ampliiier for controlling the conductivityof -said amplier overA substantiallyfany! desired portion of each cycle lof'v operationoffsaid generator, said means comprising aga'seous discharge device1 having an' anode, a grid and-acathode, 'a'` source' of unidirectional potential,-` a voltage divider connected across -said source" of i unidirectional potential, connections from l ald.-v anode4 andg'ridto-E different points on Said'f'voltagedivider, and a'conn'ection from said cathode to saidvoltagefdivlder.

`132 In" combination, asawtoothlwaine4 genera'- tor, an amplier, meanslcouplingfsaid-generator andltl'einputY ofu said amplier for controlling the 'condlictivity of saidampler'over substanl tially anyI` desired portion-ofi ealicyclefof operationfof said" generator, said'meansfcomprising a gaseousv discharge device having anAL anode, a gri'dfandf af-cathode, a :source of'v unidirectional potential; a-voltage divider Vconnected across said source of f` unidi'rectionalf potential, `connections from said'v an'o'de Y and gri'd to diieren't points* on said voltage divider, and 'a1 connectionfrom said cathode to'- said Voltage divider; thelconnection from said grid toV said:voltagedivider'being adjustableoverfsaidf'voltage divider for determining theexact'pointin saidcycleof operationrat Which the glowin said gaseous'- discharge` device' will Strikf I 14. In combination; aew'ave form generator, an amplier; ai character chopper coupling said generator "and"v lsaidamplier 'f or controlling: the conductivity ofsaid' amplifier vover 'substantiallyl any desiredfportion of each 'cycle of operationfofsaid generator-, saidchopper comprising a'fgaseous dischargedevice having an anode, a gridi-andf a cathode, a source of unidirectional'- potential, a

voltage `divider connected across" said source2 of unidirectional potential', connections` from said anode and grid to' different` points on saidivoltage divider, and-a connection from saidA cathode'V to said-voltage'divider', andan instrument in vcircuit withV thej output offsaidampli'er for' indicating the percentage lengthor AWeight of-k the marking characters-producedl in the system.

v 15. In combination, a relaxation-oscillator, an

yand ,a' connection the.v output from'` said amplifier, whereby there are' producedI signal characters inz accordance l with said interruptions, and means for controlling the weight of said signal characters.

16. In combination,aWaVe-forrn generator, an

impedance; means includingv a glow 'discharge devicefor impressing anydesired'v portion. of the voltage: Waver-oi? said generator upon saidv impedance, anamplier, an oscillator having its output coupled toV the input of said amplifier,

from said amplier to said impedance;whereby the 'conductivity of said' amplier islcontrolled" by the voltagefimpressed on said impedance;l

17. In combination, apulse generator producingipulsesiof equal length; ,an impedance; means for limpressing. the voltagewave ofsaidgenerator lupon said impedance, an amplier, an

audio frequency oscillator coupled through a circuit" of 10Wl impedance: to energy of theoscillator frequ'ency.- totherinput circuit of said amplifier, and a connectionffrom the input circuit of said ampliferl to saidimpedance, whereby the conductivity of saidramplierA is controlled bythe voltageimpressed onv saidimpedance and there are produced signal characters in the'- output of said amplifier, and means for controlling the' Weight of thesign'al characters.

18; In combinatioma relaxation oscillator, an amplifier; and al glow` discharge tube coupling said? oscillator? and said. amplifier and responsive to: theoperation of said generator Afor l'periodically. renderingf said amplifier non-conductive, and a" potentiometerincircuit With said. glow' dischargetubeffor' determining. the duration of the conductivefperiods'ofisaidamplier.

19. In combin'atiomia pulse generator, an4 am'- plier, `aniaudioV frequency oscillator Whose outputis 'coupledtothe inputvof said amplifier, an electric: tube coupling said pulse generator' and said amplifiervr and responsive to the operation ofIk saidpulsexgenerator for periodically interruptingcthe: output from saidV amplifier, whereby therefarefproduced signal characters in accordance Witlilsaid interruptions, and means for controlling thevveightv of said signal characters.

JAMES L. FINCH. 

